1. Field of the Invention
The present invention relates to an electromagnetic valve that drives a valve device by operating an electromagnetic actuator. Specifically, the present invention relates to a technology suitably applicable to an oil flow control valve (OCV) that alters a flow of oil by operating the electromagnetic actuator.
2. Description of Related Art
An oil flow control valve (OCV) is an oil pressure control valve having a spool valve (valve device) and an electromagnetic actuator. The OCV operates the electromagnetic actuator to displace a plunger in an axial direction against a biasing force of a return spring. The OCV transmits the displacement of the plunger to a spool (valve member) to displace the spool in the axial direction. Thus, the OCV switches input and output ports formed in a sleeve to control destination or intensity of an oil pressure to be supplied.
A shaft is used to transmit the axial displacement of the plunger to the spool and to transmit the axial displacement of the spool to the plunger.
In some cases, the shaft is press-fit into at least one of the spool and the plunger as disclosed, for example, in JP-A-2001-108135.
The plunger is deformed, e.g., a diameter thereof is enlarged, if the shaft is press-fit into the plunger. Therefore, an air gap, e.g., side air gap, between the plunger and a magnetic circuit, e.g., yoke, around the plunger should have some margin in consideration of the deformation (the diameter enlargement) of the plunger. Accordingly, a magnetic efficiency at the air gap decreases. Therefore, a coil for generating a magnetic force needs to be enlarged in size.
The spool is deformed if the shaft is press-fit into the spool. There is a possibility that the deformation may be transmitted to a large diameter portion (land) of the spool. A sealing portion for preventing passage of the oil is provided between the large diameter portion and the sleeve. Therefore, a clearance between the large diameter portion and the sleeve needs to be set small. However, the clearance between the large diameter portion and the sleeve needs to have some margin in consideration of the deformation (the diameter enlargement) of the large diameter portion if the deformation caused by press-fitting process is transmitted to the large diameter portion. A quantity of oil leaking through the clearance between the large diameter portion and the sleeve will increase if the clearance has a large margin.
In the case where a through hole is formed in the center of the plunger and the shaft is press-fit into the through hole, the shaft blocks the through hole. In this case, a separate respiration passage is necessary for connecting the chambers (volume changing chambers) provided on both axial sides of the plunger.
A helical groove may be formed on an outer peripheral surface of the plunger to define the respiration passage. However, a magnetic resistance is enlarged at the helical groove, so the magnetic efficiency will be deteriorated. In addition, the helical groove on the outer peripheral surface requires a complicated manufacturing process, so the cost will be increased.